This research will attempt to provide a better understanding of the role(s) of exotoxins produced by certain strains of Escherichia coli isolated from humans and neonatal animals suffering from acute diarrheal disease. At least two types of toxins appear to be important, one is heat-stable and nonantigenic, while the other is heat-labile antigenic protein. The function of each toxin in the pathogenesis of diarrheal diseases caused by enterotoxigenic strains of E. coli will be established. A defined media will be developed to optimize conditions for toxin synthesis and to study the parameters controlling toxin production. The enterotoxins will be characterized with respect to their chemical composition, subunit structure, nature of binding to intestinal mucosal cells, and the mechanism by which diarrhea results due to interaction of the toxins with epithelial cells in the intestine. Rapid and reliable diagnostic methods will be developed for detection of both toxins in culture supernatants. These methods are necessary to improve diagnosis and be a useful tool for epidemiological studies on acute diarrheal diseases.